Increased expression of galanin and its receptors in the dorsal hippocampus during epileptogenesis in a rat model of pilocarpine-induced temporal lobe epilepsy

The neuropeptide galanin has been shown to exhibit anticonvulsant effects in animal models. However, only a few studies have attempted to identify the galanin receptor subtype (s) involved in this effect. In the present study, the expression of galanin and that of its receptors in a rat model of temporal lobe epilepsy was studied to reveal the epileptogenesis-related alterations.

Pilocarpine-inducted status epilepticus (SE) rat model was used for temporal lobe epilepsy. Galanin and galanin receptor mRNA was detected by Real-time polymerase chain reaction in dorsal hippocampus of rats at three different time points following SE: at the acute phase (24h), latent period (7 days), and chronic epileptic period (8 weeks). Using immunohistochemistry, galanin positive fibers and bodies were also observed.

In the acute seizure phase, a significant up-regulation of the galanin mRNA was observed in the hippocampus. Meanwhile, galanin-positive cells appeared, while galanin-positive fibers disappeared in the hilus of the dentate gyrus, stratum radiatum of CA1, and stratum lucidum of CA3, indicating an increase in galanin synthesis and release during the acute seizure phase. The gene expression analysis also indicated a significant increase in the transcription of galanin receptors GalR1 and GalR3 24h after SE. The increased levels of GalR1 mRNA were also observed in the latent and chronic epileptic periods.

In general, these data suggest that adaptive changes occur in the galanin system during epileptogenesis that may affect its antiepileptic effects. Furthermore, these changes should be taken into account when attempting to pharmacologically modulate this system.